Hi both, thank you for taking the time to respond! 

I did a few experiments and while I figured I must've typed the wrong password once or twice -- it was a repeated problem, so I'm guessing that's not the issue. 

I don't have any interfering browsers or blocks that I can think of, although I haven't had the problem in a few days so maybe I'll leave it as is? :)

If it pops up again, I'll check it on private & will see if it's something installed. Thank you again, much appreciated!